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Tropical Storm Arthur Forecast Discussion Number 4
2020-05-17 16:45:07| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Sun May 17 2020 000 WTNT41 KNHC 171445 TCDAT1 Tropical Storm Arthur Discussion Number 4 NWS National Hurricane Center Miami FL AL012020 1100 AM EDT Sun May 17 2020 Visible satellite imagery reveals a couple of convective bands over the eastern semicircle of the tropical storm, but convection is sparse over the western portion of the circulation. The latest reports from an Air Force reconnaissance aircraft show peak 925-mb flight-level winds of 48 kt, and believable SFMR winds of 35-40 kt. On this basis, the initial wind speed has been increased to 40 kt. The plane has reported a minimum pressure of 1002-1003 mb, which is down a few millibars from the previous flight. Arthur has a little more than 24 hours in which to gradually strengthen. The storm will be traversing the relatively warm waters of the Gulf stream, and the vertical shear is forecast to remain low through early Monday. After that time, increasing shear and cooler sea surface temperatures should put a halt to the tropical cyclone strengthening processes. Baroclinic forcing is likely to help the post-tropical cyclone maintain its strengthen through extratropical transition. Later in the forecast period, the global model guidance shows weakening as the frontal gradients decrease. The storm is moving north-northeastward or 015/8 kt. Arthur is expected to begin moving a little faster later today and tonight as a mid-level trough approaches the eastern United States. Later in the forecast period, the cyclone should turn eastward within the westerly steering flow. Although the dynamical models are in agreement on the overall scenario, there remains some spread as to how close the center of Arthur will track to the North Carolina Outer Bands. The GFS and HWRF remain along the western side of the guidance while the ECMWF and UKMET bracket the eastern side. The NHC track lies near the model consensus and little change was required to the previous track through 36-48 hours. After that time, the track guidance spread increases with the ECMWF showing a much faster east-southeastward motion than the GFS. The NHC forecast remains near the consensus after 48 hours, but there is less confidence in that portion of the track prediction. Key Messages: 1. A Tropical Storm Warning is in effect for a portion of the North Carolina coast. Tropical-storm-force winds and heavy rains are expected there on Monday. 2. Dangerous coastal surf conditions and rip currents are expected to spread northward along the southeast U.S. coast to the mid-Atlantic states during the next couple of days. See products from your local National Weather Service Forecast Office for more details. FORECAST POSITIONS AND MAX WINDS INIT 17/1500Z 30.5N 77.4W 40 KT 45 MPH 12H 18/0000Z 32.0N 76.8W 45 KT 50 MPH 24H 18/1200Z 34.3N 75.5W 50 KT 60 MPH 36H 19/0000Z 36.4N 73.2W 50 KT 60 MPH 48H 19/1200Z 37.3N 70.4W 50 KT 60 MPH...POST-TROP/EXTRATROP 60H 20/0000Z 37.1N 68.2W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 20/1200Z 36.5N 66.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 21/1200Z 35.5N 64.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 22/1200Z...DISSIPATED $$ Forecaster Brown
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